>>1819789 last
A lot of it is derived out of what are called the Babylonian and Egyptian "mystery religions," which carried through into Greece and Rome. It's all in a lengthy, famous and brilliant book called The Golden Bough by Anthony Frazer.
We all see TONS of bad info on the web about how the Christian rituals and holidays were developed, and The Golden Bough, one of the original sources for comparative religion studies, explains all that, as well as the numerous and varied practices of known ancient religions.